In the drilling and completion of boreholes from a wellbore it is necessary to cement liners in place in the boreholes to enable the completion of the well for the production of fluids from the subterranean formation penetrated by the borehole. The boreholes may be lateral wells drilled from a wellbore using a whipstock at any desired angle or orientation or they may be wells which extend below the bottom of the well portion drilled by conventional means. Tubular members, such as drillpipe and coiled tubing are widely used for drilling such boreholes.
Tubular members can be used to cement a liner in place in a borehole. Typically the cement is injected through the tubular member into the liner with the cement then passing out of the end of the liner at the end of the liner and then into the annulus between the outside of the liner and the inside of the borehole. This places cement around the liner so that perforation of the formation and the like can be accomplished as well as other operations if desirable.
Typically the liner may be maintained in a central position in the borehole by the use of centralizers, as known to those skilled in the art. In such completions, the cement is passed downwardly through the tubular member and through a liner wiper plug having an opening and a passage therethrough so as to inject the cement into the liner and into the annular space around the outside of the liner and the inside of the borehole.
As the cement is injected, a cement cleanout fluid is used to push a tubular member wiper dart, which separates the cement from the cement cleanout fluid, through the tubular member downwardly and into the liner. When the cement cleanout fluid has pushed the tubular member wiper dart into the liner wiper plug, the tubular member wiper dart contacts and plugs the opening in the liner wiper plug and the combined dart/plug becomes impermeable to fluid flow into the liner, thereby resulting in the dart/plug combination being pushed through the liner and forcing the cement in the liner to its toe end and then into the annular space around the liner. The cleanout fluid is separated from the cement by the combined wiper dart and liner wiper plug. The cement cleanout fluid may be pushed through the tubular member by drilling mud or any other suitable liquid. This is a commonly used procedure to cement liners in place in subterranean boreholes and the like. Unfortunately this procedure is not suitable for use with a tubular member containing an obstruction, since the obstruction inhibits or otherwise prohibits travel of the tubular member wiper dart.
Frequently coiled tubing (a tubular member) including a wire, cable or a bundle of wires, is used for drilling lateral boreholes or other operations within the wellbore. It will be immediately apparent that the procedure just discussed is not effective to cement liners in wells using a tubular member, including a wire, since the wire makes it impossible to pass the tubular member wiper dart through the tubular member. Similarly drillpipe, which is also a suitable tubular member, is not effective when the drillpipe includes an obstruction which makes it impossible to use a drillpipe member wiper dart.
Accordingly, when tubular member drilling techniques are used it has been necessary to change out the tubular member containing the wire for a tubular member containing no wire prior to cementing liners into place. This has been a necessary operation and can be quite expensive and time consuming. The cost to make this exchange has been estimated to typically run in the neighborhood of $100,000 per exchange.
Accordingly a continuing effort has been made to discover ways of cementing liners in boreholes using tubular members containing obstructions without changing out the tubular members containing obstructions.